diff --git a/src/pretix/api/serializers/organizer.py b/src/pretix/api/serializers/organizer.py
index 754dc2d657..6389298df7 100644
--- a/src/pretix/api/serializers/organizer.py
+++ b/src/pretix/api/serializers/organizer.py
@@ -570,6 +570,7 @@ class OrganizerSettingsSerializer(SettingsSerializer):
         # should not be included!
         'customer_accounts',
         'customer_accounts_native',
+        'customer_accounts_to_oidc',
         'customer_accounts_link_by_email',
         'customer_accounts_require_login_for_order_access',
         'invoice_regenerate_allowed',
diff --git a/src/pretix/base/settings.py b/src/pretix/base/settings.py
index ec6224e768..7195465216 100644
--- a/src/pretix/base/settings.py
+++ b/src/pretix/base/settings.py
@@ -181,6 +181,19 @@ DEFAULTS = {
             widget=forms.CheckboxInput(attrs={'data-display-dependency': '#id_settings-customer_accounts'}),
         )
     },
+    'customer_accounts_to_oidc': {
+        'default': 'False',
+        'type': bool,
+        'form_class': forms.BooleanField,
+        'serializer_class': serializers.BooleanField,
+        'form_kwargs': dict(
+            label=_("Convert existing customers to single-sign-on accounts when logging in through single-sign-on provider"),
+            help_text=_(
+                "If disabled, pretix does not allow to log in through a single-sign-on provider if the customer is registered with email and password."
+            ),
+            widget=forms.CheckboxInput(attrs={'data-display-dependency': '#id_settings-customer_accounts'}),
+        )
+    },
     'customer_accounts_require_login_for_order_access': {
         'default': 'False',
         'type': bool,
diff --git a/src/pretix/control/forms/organizer.py b/src/pretix/control/forms/organizer.py
index 0078562506..d91b3e685d 100644
--- a/src/pretix/control/forms/organizer.py
+++ b/src/pretix/control/forms/organizer.py
@@ -600,6 +600,7 @@ class OrganizerSettingsForm(SettingsForm):
         'allowed_restricted_plugins',
         'customer_accounts',
         'customer_accounts_native',
+        'customer_accounts_to_oidc',
         'customer_accounts_link_by_email',
         'customer_accounts_require_login_for_order_access',
         'invoice_regenerate_allowed',
diff --git a/src/pretix/control/templates/pretixcontrol/organizers/edit.html b/src/pretix/control/templates/pretixcontrol/organizers/edit.html
index 960c6fb4f5..010c1901b5 100644
--- a/src/pretix/control/templates/pretixcontrol/organizers/edit.html
+++ b/src/pretix/control/templates/pretixcontrol/organizers/edit.html
@@ -132,6 +132,7 @@
                         <legend>{% trans "Customer accounts" %}</legend>
                         {% bootstrap_field sform.customer_accounts layout="control" %}
                         {% bootstrap_field sform.customer_accounts_native layout="control" %}
+                        {% bootstrap_field sform.customer_accounts_to_oidc layout="control" %}
                         {% bootstrap_field sform.customer_accounts_require_login_for_order_access layout="control" %}
                         {% bootstrap_field sform.customer_accounts_link_by_email layout="control" %}
                         {% bootstrap_field sform.name_scheme layout="control" %}
diff --git a/src/pretix/presale/views/customer.py b/src/pretix/presale/views/customer.py
index 5e15cfe442..b002711a6f 100644
--- a/src/pretix/presale/views/customer.py
+++ b/src/pretix/presale/views/customer.py
@@ -864,11 +864,36 @@ class SSOLoginReturnView(RedirectBackMixin, View):
                         identifier=identifier,
                     )
                 except Customer.DoesNotExist:
-                    return self._fail(
-                        _('We were unable to use your login since the email address {email} is already used for a '
-                          'different account in this system.').format(email=profile['email']),
-                        popup_origin,
-                    )
+                    # no race-condition, try to convert to oidc?
+                    if self.request.organizer.settings.customer_accounts_to_oidc:
+                        try:
+                            customer = self.request.organizer.customers.get(
+                                email=profile['email'],
+                            )
+                            update_fields = {
+                                'provider': self.provider.pk,
+                                'external_identifier': str(profile['uid']),
+                                'identifier': identifier,
+                                'is_active': True,
+                                'is_verified': True,
+                            }
+                            if name_parts:
+                                update_fields['name_parts'] = name_parts
+                            if profile.get('phone'):
+                                update_fields['phone'] = profile.get('phone')
+                            customer.update(**update_fields)
+                        except Customer.DoesNotExist:
+                            # should actually never happen
+                            return self._fail(
+                                _('We were unable to use your login since either the email address is unknown in this system.'),
+                                popup_origin,
+                            )
+                    else:
+                        return self._fail(
+                            _('We were unable to use your login since the email address {email} is already used for a '
+                              'different account in this system.').format(email=profile['email']),
+                            popup_origin,
+                        )
         else:
             if customer.is_active and customer.email != profile['email']:
                 customer.email = profile['email']